Why serve function runs twice when app is reloaded?

[ShehanIshanka]

Is there any reason for running serve function twice when app is reloaded?

Sample code

from h2o_wave import main, app, Q, ui

@app('/')
async def serve(q: Q):
    print("Testing......")
    content = 'Welcome to our store!'

    location = q.args['#']
    if location:
        if location == 'menu/spam':
            content = "Sorry, we're out of spam!"
        elif location == 'menu/ham':
            content = "Sorry, we're out of ham!"
        elif location == 'menu/eggs':
            content = "Sorry, we're out of eggs!"
        elif location == 'about':
            content = 'Everything here is gluten-free!'

    if not q.client.initialized:
        q.page['nav'] = ui.tab_card(
            box='1 1 4 1',
            items=[
                ui.tab(name='#menu/spam', label='Spam'),
                ui.tab(name='#menu/ham', label='Ham'),
                ui.tab(name='#menu/eggs', label='Eggs'),
                ui.tab(name='#about', label='About'),
            ],
            value=f'#{location}' if location else None,
        )
        q.page['blurb'] = ui.markdown_card(
            box='1 2 4 2',
            title='Store',
            content=content,
        )
        q.client.initialized = True
    elif location:
        blurb = q.page['blurb']
        blurb.content = content

    await q.page.save()

Log

INFO:     127.0.0.1:56126 - "POST / HTTP/1.1" 200 OK
Testing......
INFO:     127.0.0.1:56126 - "POST /disconnect HTTP/1.1" 200 OK
2023/07/12 15:23:10 # {"addr":"[::1]:56079","t":"ui_drop"}
INFO:     127.0.0.1:56126 - "POST / HTTP/1.1" 200 OK
Testing......
2023/07/12 15:23:11 # {"addr":"[::1]:56127","route":"/","t":"ui_add"}
2023/07/12 15:23:11 # {"addr":"[::1]:56127","route":"/b14664c5-5a5a-476e-8389-81ea59784829","t":"ui_add"}
2023/07/12 15:23:11 * /b14664c5-5a5a-476e-8389-81ea59784829 {"d":[{"k":"nav","d":{"view":"tab","box":"1 1 4 1","items":[{"name":"#menu/spam","label":"Spam"},{"name":"#menu/ham","label":"Ham"},{"name":"#menu/eggs","label":"Eggs"},{"name":"#about","label":"About"}]}},{"k":"blurb","d":{"view":"markdown","box":"1 2 4 2","title":"Store","content":"Welcome to our store!"}}]}

cc @dulajra

[mturoci]

Yes, the reason is that when reload is hit, the first serve corresponds to client disconnect and the second one is the initial serve call.

[Nayananga]

@mturoci We have a specific use case where we need to obtain the browser timezone, here I have shared a sample code with our workaround to get the browser timezone while using WAVE. This is causing the serve function to run one more time totaling thrice when reloading the app. Is there a better way to get the browser timezone without triggering the serve function?

from h2o_wave import main, app, Q, ui, on, handle_on


@on()
async def button_click(q: Q):
    q.page["meta"].notification_bar = ui.notification_bar(
        text=f'you timezone is {q.client.timezone}',
        type='success',
        position=ui.NotificationBarPosition.TOP_CENTER,
    )


@on("global_events.set_timezone")
async def window_loaded(q: Q) -> None:
    q.client.timezone = q.events.global_events.set_timezone


def resolve_timezone() -> str:
    return """
                wave.emit(
                    "global_events",
                    "set_timezone",
                    Intl.DateTimeFormat().resolvedOptions().timeZone
                );
            """


@app('/')
async def serve(q: Q):
    if not q.client.initialized:
        q.client.initialized = True
        q.page['meta'] = ui.meta_card(
            box='',
            layouts=[
                ui.layout(
                    breakpoint="xs",
                    zones=[
                        ui.zone(
                            name="body",
                            direction=ui.ZoneDirection.ROW,
                        ),
                    ],
                )
            ],
            script=ui.inline_script(resolve_timezone(), requires=[])
        )

    q.page['body'] = ui.form_card(box='body', items=[
        ui.button(name='button_click', label='Button Click'),
    ])

    await handle_on(q)

    await q.page.save()

[mturoci]

This is causing the serve function to run one more time totaling thrice when reloading the app.

How many times would you expect it to run?

1. Disconnect from previous load.
2. Initial serve.
3. JS callback to get the timezone.

Is there a better way to get the browser timezone without triggering the serve function?

Please let's discuss one topic at a time in order to not bloat the discussion thread. Open a new discussion for completely new topics.

[Nayananga]

@mturoci raised here #2096